The concept of enhancing electrolyte convection in an electrowinning or electrorefining cell to generally improve the results of metallic electrodeposition by means of controlled gas diffusion from a horizontal plane near the bottom and under the electrodes of the cell has been know for many years. Both the quality of the metal electrodeposited in the harvested cathode as well as the productivity of each cell—by effect of higher current density applicable to the process without quality compromises—are considerably increased applying especially soft aeration to the process in each cell.
In the prior art, there are several designs of apparatus that allow diffusing low pressure gas bubbles inside an electrolytic cell. One of them is by means of an isobaric ring fitting the internal normally rectangular perimeter of the cell generally improves the results of metallic electrodeposition, These rings are formed by straight tubes of circular cross section connected in rectangular manner, to conduct the dosed gas at low pressure throughout its interior, generating bubbles upon emerging uniformly from the lower horizontal plane under the electrodes of the cell and rising to the surface of the electrolyte. For that purpose, the opposite sides of said rectangular ring are connected transversally from side to side with perforated tubes, microporous or microperforated hoses, from Which gas bubbles emerge at low pressure through the perforations of the tubes or hoses, With given initial diameters—that increase as the bubbles ascend to the electrolyte surface—because of the gradually diminishing pressure of the electrolyte column over the bubbles as they rise.
There are several patent documents that disclose solutions to the provision of bubbles of saturated gas or air to the electrolyte of an electrowinning or electrorefining cell.
Document U.S. Pat. No. 1,260,830, published Mar. 26, 1918, titled “Electrolytic deposition of copper from acid solutions” discloses copper electrodeposition by means of continuous agitation of the electrolyte, particularly sweeping the surface of the vertical anodes with a mixture of sulfur dioxide gas and vapor, projected from orifices perforated in transversal lead pipes, disposed parallel to and under the anodes in the cell, with the orifices oriented in such a manner that the fluid emerges in an oblique angle striking the surface of the anodes, forcing continually the electrolyte circulation with maximum agitation and turbulence occurring by impact of the mixture directly on the faces of the anodes.
Document U.S. Pat. No. 3,928,152, published Dec. 23, 1975, titled “Method for the electrolytic recovery of metal employing improved electrolyte convection”, describes a method of high quality copper electrodeposition on permanent cathodes plates at very high current densities. To achieve high productivity the separation between electrodes is reduced to a minimum with separators—distancers that position them exactly relative to each other, and simultaneously, provide very aggressive continuous agitation of the electrolyte by gas sparging tubes placed under each cathode, disposed to sweep the faces of the cathodes with curtains of bubbles that emerge from holes perforated in the tubes.
Document U.S. Pat. No. 3,959,112 published May 25, 1976, under the title “Device for providing uniform air distribution in air-agitated electrowinning cells”, discloses air bubbling devices placed transversely to the cell length parallel on both faces of the cathodes just below their lower edge. The device comprises rigid perforated tubes that allow discharging air in bubbles of relatively large diameter with minimum pressure loss, whereby said tubes are enclosed externally with sleeves of larger diameter permeable material that oppose resistance and restrict the passage of the air bubbles, forcing them to emerge continuously from the sleeves as curtains of very fine bubbles that then sweep vertically both faces of the cathode and thus inhibiting the formation of rugosities on the metal deposit.
U.S. Pat. No. 4,263,120, published Apr. 21, 1981, under the title “Electrolytic cell for the recovery of non ferrous metals and an improved anode therefor”, discloses the operation of the process with electrolyte agitation by means of perforated gas bubbler tubes placed parallel under the anodes to create ascending electrolyte turbulence in the interfaces of the electrodes.
Document CL 527-01, published Sep. 27, 2002, today patent CL 44.803 titled “System and method to capture and extract acid mist from polymer concrete containers, were the side, frontal and back walls are modified to allow horizontal seat of a thermal cover that forms a chamber connected to extraction ducts, method of fabrication and container for such purpose”, discloses an electrolytic cell that comprises among other elements, a duct for injection of fresh air with gas diffusers installed parallel, and in a plane in the inferior portion of the cell, that directs the air bubbles under the electrodes.
Document CL 2140-2004, published Jul. 27, 2006, (equivalent to document WO 2005/019502) titled “Method to operate and electrolytic cell . . . ” discloses gas diffusers for the transfer by gas bubbling to liquid means comprising an element consisting of a body of cylindrical connection that is prolonged in a tube conical zone ending in a closed end; between the cylindrical zone and the end zone there is a multi perforated separation wall trough which from the interior of the cylindrical body air circulates at constant pressure and velocity, generating a gas stream that distributes forming gas minijets.
Document CL 727-2006 published Jul. 7, 2006, titled “Electrolyte agitating device that consists of a reticulated structure, flat and of regular plant, formed of non electric conducting polymer composite materials resistant to corrosion, and, comprising an isobaric gas distribution ring, gas diffuser means; and electrolyte agitation system”, discloses an electrolyte agitation apparatus immersed in containers for electrolytic cell used in the processes of electrowinning and electrorefining of non ferrous metal, formed by pipes of anticorrosive and non conducting materials, joined by connecting elements, were said joined pipes are crossed over from one side to the other by gas diffuser means, were said joined pipes and connected elements form and isobaric ring, which is encapsulated in the interior of a shape formed monolithically of anticorrosive dielectric polymer composite material, forming one flat, perimetral parallelepiped structure, homologous to the shape of the bottom of the container, where said perimetral structure is reticulated to impart rigidity and necessary structural resistance to be self supporting.
Document CL 0025-2008 published Mar. 18, 2008, discloses an aeration system by microbubbles for the electrowinning of copper at high current density, comprising independent pipes for the electrolyte, and connected together by spray nozzles for jetting the mixture of electrolyte-air to the interior of the cell and a line of aspiration and a pulse generator.
Document CL 00642-2007, published Oct. 26, 2007, describes equipment for the circulation of electrolyte and gases in an electrolytic cell, comprises perforated tubing for the circulation of electrolyte and one or more circuit of perforated tubing for gas injection affixed to a supporting structure with a plurality of guides for anodes and cathodes allowing the introduction and retrieval from the cell.
In general, in all prior art described, notwithstanding advantages disclosed in the results of electrodeposition with air bubbles sparged in the electrolyte, all solutions disclosed are oriented to describing the supply of aereation inside a single cell. None of the documents cited approaches the problem involved in generating air centrally and distributing air dosed exactly to each individual cell in a group of cells, in a bay of cells or in general, in an electrowinning or electrorefining plant, where each electrolytic cell demands an individual predetermined air flow.
In industrial electrowinning or electrorefining plants, the aereation equipment used in the cells can—abruptly or progressively—change its pneumatic characteristics within its service life, thereby requiring systematic individual adjustment or replacement whenever the original characteristics are lost or as they get damaged by other causes. It is well known in the art that successful operation of the cells require harmonization of several operational parameters until the desired electrodeposition results are obtained; and once established, such harmony must be duly adjusted and controlled in time following an operational management protocol of principal variables such as: cell voltage, current density, electrolyte temperature, copper tenor, pH and flow, among others. It is these parameters that determine the quality of copper deposit obtained on the cathodes at harvest time. With the introduction of gentle aereation in the cells an additional parameter is added to the operational management protocol that also needs the same harmonization, control and adjustment together with the others just mentioned, such as the homogeneous and controlled gas diffusion, preferably air, from a horizontal plane near the bottom of the cell under the electrodes, enhancing convection that favors the results of metallic electrodeposition. In practice, all these parameters are adjusted according to the electrodeposition results actually obtained on the cathodes. In as much as the overall cathode metal quality improves, the parameters are maintained stable during the operation of the cell, and are only adjusted to overcome unfavorable trends in the quality of harvested cathodes. The variability depends not only on the parameters of the generic electrodeposition process but also on the condition of wear and tear, useful life and replacement of the cell proper and its associated equipment. This explains the difficulty and complexity in correctly harmonizing these parameters well for each cell within a plant, specially maintaining them steady and uniform in each cell, and therefore, it is absolutely necessary to provide means, systems and methods for constantly monitoring them in real time. Accordingly by the facts presented, the volume of air that each individual cell demands is variable in time according to the pneumatic characteristics of its diffusion mean, and therefore, it becomes necessary to determine for each cell, the optimal flow that each must receive so as to obtain uniform and sustained electrodeposition results from all the cells in a plant.